Roll PDFium from 40d3f47d189c to 5b4eaf71f78b (4 revisions)

https://pdfium.googlesource.com/pdfium.git/+log/40d3f47d189c..5b4eaf71f78b

2020-09-16 thestig@chromium.org mac arm64: Use the correct page size for this platform in PartitionAlloc
2020-09-15 thestig@chromium.org Download the selected version of hermetic Xcode via custom_vars.
2020-09-15 tsepez@chromium.org Rework pdf_fuzzer_init_public.cc
2020-09-14 thestig@chromium.org Remove unused RenderDeviceDriverIface methods.

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/pdfium-autoroll
Please CC pdfium-deps-rolls@chromium.org on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Bug: chromium:1128457
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I9450d2b37c49846415ecee7bf552a8daf0d09b41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412978Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#807348}

DEPS

@@ -215,7 +215,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.
-  'pdfium_revision': '40d3f47d189c1ac36b14f3fe6d6ba9ce4c0a7d7e',
+  'pdfium_revision': '5b4eaf71f78bdb2e1c8b88a84eba68510dd871ac',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.